The gastrointestinal tract is exposed to microbial pathogens and other environmental stresses. The long-term objective of these studies is to determine the role of NF-kappaB and the MAP kinase signaling pathways in intestinal mucosal innate defense and injury. These studies use in vitro and in vivo model systems and genetic, genomic and biochemical approaches to address five Specific Aims: Aim 1 uses a genetic approach in an in vivo model of ischemia-reperfusion injury in mice to determine which cells in the intestinal mucosa respond to ischemiareperfusion and cause systemic inflammation through the activation of NF-kappaB and NF-kappaB target genes. These experiments use models in which the IkappaB kinase beta gene required for signal-induced activation of NF-kappaB has been conditionally deleted in intestinal epithelial cells or in macrophages. Macrophages are a critical cell type for host innate immunity to microbial pathogens. We show that inhibiting p38 MAP kinase markedly increases activationinduced death of macrophages in response to LPS signaling through Toll-like receptor (TLR) 4. Aims 2-4 address the mechanisms by which p38 MAP kinase and NF-kappaB govern apoptotic cell death in macrophages. Aim 2 uses a molecular and biochemical approach to determine the mechanism by which inhibition of p38 MAPK activation in macrophages sensitizes those cells to TLR-dependent activation-induced death. Aim 3 uses a directed functional genomic approach to identify the anti-apoptotic genes expressed in macrophages that are co-regulated by the NF-kappaB and p38 signaling pathways and that induce resistance to activation-induced death in those cells. Aim 4 proceeds to identify the mechanism of transcriptional synergy through which NF-kappaB and p38 in macrophages cooperate to activate the transcription of anti-apoptotic and proinflammatory genes. Since inducing apoptosis of macrophages is a key strategy of microbial pathogens to avoid host innate immune defense, studies in Aim 5 will determine the interacting mechanisms used by a clinically significant enteric pathogen, Salmonella, to causes macrophage apoptosis in order to subvert host innate defense. By elucidating mechanisms of host mucosal innate resistance to microbial infection and intestinal injury and the strategies used by microbes and their products to subvert host mucosal defense, these studies have significant implications for the development of novel strategies to prevent and treat intestinal inflammatory and infectious diseases in the intestinal tract.